Matthew Ballister, who is accused of killing his girlfriend, now faces charges of threatening her and desecrating her remains, as well as hindering the police investigation.Patti Sapone/The Star-Ledger

ELIZABETH — On the night that Matthew Ballister allegedly killed his girlfriend, he attacked her in her car and then held her prisoner "for a substantial period of time," intending to injure or terrorize her, according to court papers obtained yesterday.

Ballister, 43, of Union Township, is also accused of using "force" to prevent witnesses from giving information to police. But the documents do not say who the witnesses are, or what kind of information they had.

Police arrested Ballister on Oct. 23 and charged him with murdering April Wyckoff, 43, of Cranford, the previous night in his home.

Police made the arrest even though they had not yet found Wyckoff’s body. On Oct. 28, authorities announced that body parts found the previous day along the edge of the Passaic River in Newark belonged to Wyckoff.

Police continued to search for additional remains earlier this week, the Union County Prosecutor’s office said.

April WyckoffFacebook

Last week, authorities filed additional charges against Ballister, including felony murder charges for allegedly killing Wyckoff while restraining her. Ballister also faces two counts of desecration of human remains, and single counts of kidnapping, making terroristic threats and criminal restraint.

According to a complaint filed in Superior Court, Ballister entered Wyckoff’s car to attack her, threatened to kill her, and restrained her in his house.

Ballister also obstructed witnesses from providing authorities information "by means of force," according to the complaints. They state that Ballister also lied to police.

The additional charges are based on statements from witnesses, video from surveillance cameras and a search of Ballister’s home and his vehicle, a Hummer H2, court papers state.

The prosecutor’s office did not immediately respond to requests for comments about the complaints.

Ballister is being held at the Union County jail in Elizabeth in lieu of $5.5 million bail. A lawyer who attended Ballister’s initial court appearance said the defendant will plead not guilty.

Ballister’s mother, Eleanor Schofield, 70, of Mountainside, was also arrested and has pleaded not guilty to a charge of hindering the police investigation. She has been accused of helping to hide evidence.